The invention relates to the protection of structural fasteners and assemblies from environmental exposures. The invention relates in general to “wind generator” applications, although it will be readily apparent that the present invention may be utilized in many other types of structures and applications, and the invention is by no means limited to wind generator applications. Wind generators are used in the generation of electricity through the rotation of turbines and conventionally feature a plurality of propellers or blades arrayed high enough above the ground to be responsively compelled into rotation by naturally occurring wind.
In one common style of wind generator, a tower structure is provided (conventionally about 200 feet high or higher), at the top of which is an array of large propellers or blades (conventionally about 90 feet or longer) which are rotated by the wind forces, thereby generating electricity. Referring now to FIGS. 1 and 2, views of a typical prior art wind tower installation are provided. The bottom end of a wind generator tower base 10 is attached to a base foundation 20 firmly installed into the earth, typically 30 feet or more deep, through a plurality of anchor bolts 16. A door 12 gives access to the interior of the tower base. An annular flange 14 is formed on the bottom end of tower base 10. The top ends of anchor bolts 16 extend at least 10 inches above the top surface of flange 14 and each has a nut 18 threaded thereon. A concrete walk 19 extends around the perimeter of tower base 10. The base foundation 20 is covered by dirt 21.
FIG. 2 is a sectional side elevation view of base foundation 20. It is formed on site in a hole approximately 30 feet deep and about 10-15 feet in diameter. A metal embedment ring 23 is placed in the base foundation hole spaced a predetermined distance above the bottom of the hole. Approximately 250 anchor bolts 16 have their bottom ends captured in apertures in the embedment ring and have a nut threaded onto their bottom end. The anchor bolts are oriented in two concentric circular patterns. Each of the anchor bolts 16 has a tubular conduit 40 slid over them to protect them from concrete that is later poured between cylinder inner metal form 25 and cylinder outer metal form 27. Horizontally spaced rebar hoops 29 maintain the anchor bolts in their proper alignment. Spacer rods 31 are located at various positions to keep the respective inner and outer metal forms 25 and 27 in their proper positions. Outer metal form 27 is longer than inner metal form 25 so that when concrete 33 is poured between the respective forms, it will travel downwardly and centrally to form a concrete bottom wall 35. Dirt is filled into the area within the center of metal form 25. A metal template ring 37 has an outer and inner circular pattern of apertures for receiving the top ends of the respective anchor bolts 16. The top surface of metal template ring 37 forms an annular trough that is later filled with grout. When the grout has properly set, the bottom end of tower base 10 is erected on the top surface of metal template ring 37 with the respective top ends of the anchor bolts 14 passing through the respective apertures in the inner flange (not shown) and outer flange 14 in the manner illustrated in FIG. 1.
In a typical prior art installation, the nuts 18 are screwed on the top end of anchor bolts 16, following which a second nut is then threaded onto “the top end” of the respective anchor bolts, and hydraulic jacks are attached thereto so that the anchor bolts can be stressed to approximately 70 to 80 thousand pounds of stress. At this time, the lower nuts 18 are cinched down and the hydraulic jacks and their associated nuts are removed.
It is common for wind generators and their associated tower base assemblies to provide for an expected service lifespan of between 20 and 30 years. However, of particular concern over the anticipated lifespan of the tower base assembly is the effect of corrosion of structural materials due to environmental exposure. Anchor rod bolts 16 are typically fabricated from high-strength metal “rebar” source material, and anchor rod nuts 18 are also typically fabricated from high-strength metallic source materials. It is well known that many high-strength metal source materials experience oxidation and/or other corrosion degradations responsive to exposure to moisture and oxidizing air and other gases. Accordingly, anchor rod and nut surfaces exposed to moisture will experience corrosion degradation over time, which may be severe enough to reduce the serviceable lifespan of either or both of the anchor rod bolt and nut to a period significantly less than the serviceable life of a wind tower generator.
Specifically, the top ends of the anchor bolt assemblies are exposed to environmental corrosion-causing or enabling elements, such as sun, wind, rain, snow and moisture. The anchor rod 16 which surfaces below the base flange 14 must also be protected from oxygen, moisture, environmental exposure and other agents that may enter the air space between the anchor rod 16 and the tubular conduit 40 and cause degradation of anchor rod surfaces protective coverings. Without adequate waterproofing measures, water and condensing moisture may enter along the bottom surfaces of the wind tower base flange and seep down from the bottom surface areas of the wind tower foundation and into the lower anchor rod 16 and base foundation tubular conduit 40 assembly. Air may also be admitted, resulting in oxygen or air-entrained moisture attack on the anchor rod 16 surfaces below the base flange 14. Such corrosion degradation may weaken an anchor rod 16 and thereby significantly shorten the effective life of a wind generator tower base. Therefore, it is important to prevent the introduction of corrosive agents, such as air, moisture and water onto the exposed anchor rod 16, nut 18, washer 20 and upper flange surface 14 structures above the flange 14. It is also important to prevent the introduction of corrosive agents onto surface areas of the anchor rod 16 throughout its entire structural length below the wind tower base flange 14.
One solution for this problem is to cover the exposed anchor bolts 16 and nuts 18 with a film of grease to keep them protected from attack by oxygen or moisture in the air. However, the grease-film layer must itself be protected in order to keep the layer intact during the service life of the anchor bolt and nut assembly. Environmental erosion factors including wind, sun, rain and snow, and/or grazing livestock, wild animals or human tampering may remove all or part of the protective grease-film layer, thereby exposing the metal surfaces and resulting in oxidation corrosion damage to the assembly. Also, an exposed anchor nut 18 and bolt 16 assembly may invite vandalism and tampering with the assembly.
Accordingly, what is needed is an additional physical protective barrier structure that will protect the water and gas-resistant film layers commonly deposited on anchor nut 18 and rod 16 assemblies, thereby preventing corrosion over the serviceable life of the anchor rod and base flange assembly structures.